High sensitivity semiconductor device for detecting fluid chemical species and related manufacturing method

ABSTRACT

A device for detecting a chemical species, including a Geiger-mode avalanche diode, which includes a body of semiconductor material delimited by a front surface. The semiconductor body includes: a cathode region having a first type of conductivity, which forms the front surface; and an anode region having a second type of conductivity, which extends in the cathode region starting from the front surface. The detection device further includes: a sensitive structure arranged on the anode region and including at least one sensitive region, which has an electrical permittivity that depends upon the concentration of the chemical species; and a resistive region, arranged on the sensitive structure and electrically coupled to the anode region.

BACKGROUND Technical Field

The present disclosure relates to a high sensitivity semiconductordevice for detecting fluid chemical species, as well as to the relatedmanufacturing method.

Description of the Related Art

As is known, in various fields of application there is today a desire todetect one or more chemical species, in particular in the gaseous phase,and hence determine the corresponding concentrations of such chemicalspecies. For instance, in the field of the automotive industry, there isa desire to determine the concentrations, within an exhaust gas, ofchemical species that are generated in the course of the thermalreactions that occur within an engine. In this connection, it is knownthat, following upon a reaction of combustion that takes place betweenthe fuel and the air, water (H₂O) and pollutant chemical species, suchas carbon dioxide (CO₂), carbon monoxide (CO), sulphur oxides (SO_(x)),nitrogen oxides (NO_(x)), hydrocarbons (HC), and particulate matter(PM), are generated. In turn, nitrogen oxides include nitrogen monoxide(NO), nitrogen dioxide (NO₂), and dinitrogen monoxide (N₂O).

Once again by way of example, there is today a desire to have availablesensors that enable detection of volatile organic compounds (VOCs),which are highly pollutant, in order to detect the quality of the air.In this connection, volatile organic compounds comprise, among otherthings, the so-called aromatic polycyclic hydrocarbons (APHs), thelatter being notoriously dangerous for human health.

Irrespective of the field of application, and hence of the particularchemical species that are to be measured, various detection methods havebeen developed, which broadly speaking may be divided into: i) methodsbased upon detection of the variations of an electrical quantity of asensitive element, following upon interaction between the sensitiveelement and the chemical species under examination; and ii) methodsbased upon detection of variations of quantities of a non-electricaltype, such as acoustic quantities, optical quantities, etc.

Considering merely sensors that are based upon the variation of anelectrical characteristic of a sensitive element thereof, they arecharacterized by low costs and by a certain simplicity of construction;however, they are likewise characterized by a not particularly highsensitivity, as well as, at times, by relatively long response times. Inthis connection, in general by “response time” is meant the time thatelapses between the instant when the chemical species under examinationreaches a threshold level and a subsequent instant, when the sensordetects that the threshold level has been reached.

BRIEF SUMMARY

One or more embodiments of the present disclosure provide asemiconductor device for detecting fluid chemical species that willsolve at least in part the drawbacks of the prior art.

According to the present disclosure, a semiconductor device includes:

a body of semiconductor material delimited by a front surface;

a Geiger-mode avalanche diode, including:

-   -   a cathode region of a first type of conductivity formed in the        body and extending from the front surface; and    -   an anode region of a second type of conductivity, which extends        in the cathode region starting from the front surface;

a sensitive structure arranged on the anode region and including asensitive region, said sensitive region having an electricalpermittivity that depends upon a concentration of said chemical species;and

a resistive region arranged on the sensitive structure and electricallycoupled to the anode region.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

For a better understanding of the present disclosure, preferredembodiments thereof are now described, purely by way of non-limitingexample and with reference to the attached drawings, wherein:

FIGS. 1, 7, 8, 9, and 10 are schematic cross-sectional views ofembodiments of the present detection device;

FIG. 2 is a schematic perspective view of an array of detection devices;

FIG. 3 is a schematic top plan view with portions removed of theembodiment illustrated in FIG. 1 ;

FIGS. 4A and 4B each show time plots of current pulses for differentvalues of the capacitance of a sensing capacitor;

FIG. 5 shows a block diagram of a system for detecting chemical species;

FIG. 6 shows an example of plot of the duration of a time interval, as afunction of a variation of a value of capacitance; and

FIGS. 11-20 are schematic cross-sectional views of a detection device,during successive steps of a manufacturing method.

DETAILED DESCRIPTION

The present semiconductor device is based upon the principle ofoperation of Geiger-mode avalanche photodiodes (GMAPs), also known assingle-photon avalanche diodes (SPADs), in so far as they are able, atleast theoretically, to ensure detection of individual photons.

In detail, it is known that a SPAD comprises a junction made ofsemiconductor material, which has a breakdown voltage V_(B) and isbiased, in use, at a reverse-biasing voltage V_(A) higher in modulusthan the breakdown voltage V_(B). In this way, the junction presents aparticularly extensive depleted region, present in which is anon-negligible electrical field. Hence, generation of a singleelectron-hole pair, caused by absorption within the depleted region of aphoton incident on the SPAD, may be sufficient for triggering anionization process. This ionization process in turn causes an avalanchemultiplication of the carriers, with gains of around 10⁶, and consequentgeneration in short times (hundreds of picoseconds) of the so-calledavalanche current, or more precisely of a pulse of the avalanchecurrent.

The avalanche current can be collected by means of an external circuitryconnected to the junction and represents a signal generated by the SPAD,also referred to as “output current”. In practice, for each photonabsorbed, a pulse of the output current of the SPAD is generated.

The fact that the reverse-biasing voltage V_(A) is higher, in modulus,than the breakdown voltage V_(B) causes the avalanche-ionizationprocess, once triggered, to be self-sustaining. Consequently, once theavalanche-ionization process has been triggered, the SPAD is no longerable to detect photons, with the consequence that, in the absence ofappropriate remedies, the SPAD manages to detect arrival of a firstphoton, but not arrival of subsequent photons. To be able to detect alsothe subsequent photons, it is necessary to quench the avalanche currentgenerated within the SPAD, thus arresting the avalanche-ionizationprocess, and in particular lowering, for a period of time known as“hold-off time”, the effective voltage V_(e) across the junction, so asto inhibit the ionization process. For this purpose, there is known theuse of so-called quenching circuits, which may be of an active orpassive type. Then, the reverse-biasing voltage V_(A) is restored inorder to enable detection of a subsequent photon.

This having been said, the present applicant has noted how it ispossible to modify the structure of a SPAD so as to achieve thepossibility of modulating the shape of the time plot of the pulses ofthe avalanche current as a function of the concentration of one or morechemical species under examination.

In greater detail, FIG. 1 shows a detection device 1, which isintegrated in a die 100 of semiconductor material. As illustrated inFIG. 2 , the detection device 1 may form part of an array 220 ofdetection devices that are the same as one another, all designated by 1.

In detail, the detection device 1 comprises a semiconductor body 3,which is made, for example, of silicon and in turn comprises a substrate2, delimited by a bottom surface S_(inf). Moreover, the detection device1 includes a first epitaxial layer 6 and a second epitaxial layer 8. InFIG. 1 , the thicknesses of the substrate 2 and of the first and secondepitaxial layers 6, 8 are not in scale, as neither are the thicknessesof the other regions, described hereinafter.

The substrate 2 is of an N++ type, has a thickness of, for example,between 300 μm and 500 μm, and has a doping level of, for example,between 1·10¹⁹ cm⁻³ and 1·10²⁰ cm⁻³.

The first epitaxial layer 6 is of an N+ type, has a thickness of, forexample, between 4 μm and 8 μm and overlies, in direct contact, thesubstrate 2. Moreover, the first epitaxial layer 6 has a doping levelof, for example, between 1·10¹⁶ cm⁻³ and 5·10¹⁶ cm⁻³.

The second epitaxial layer 8 is of an N− type, has a thickness of, forexample, between 3 μm and 5 μm and overlies the first epitaxial layer 6,with which it is in direct contact. Moreover, the second epitaxial layer8 has a doping level of, for example, between 1·10¹⁴ cm⁻³ and 3·10¹⁴cm⁻³. Moreover, the second epitaxial layer 8 forms a top surfaceS_(sup), which delimits the semiconductor body 3.

An anode region 12, of a P+ type, which has, in top plan view, acircular or polygonal (for example, quadrangular) shape, gives out ontothe top surface S_(sup) and extends in the second epitaxial layer 8. Inparticular, the anode region 12 has a thickness of, for example, between0.05 μm and 0.4 μm; moreover, the anode region 12 has a doping level of,for example, between 1·10¹⁸ cm⁻³ and 1·10¹⁹ cm⁻³.

An enriched region 14, of an N type, extends in the second epitaxiallayer 8, underneath, and in direct contact with, the anode region 12. Intop plan view, the enriched region 14 has a circular or polygonal (forexample, quadrangular) shape; moreover, the enriched region 14 has athickness of, for example, 1 μm and a doping level of, for example,between 1·10¹⁶ cm⁻³ and 5·10¹⁶ cm⁻³.

For practical purposes, the anode region 12 and the enriched region 14form a first PN junction, designed to receive photons and generate theavalanche current. The enriched region 14 and the second epitaxial layer8 have, instead, the purpose of confining a high electrical field in theproximity of the first PN junction, reducing the breakdown voltage V_(B)of the junction itself.

A guard ring 16 having a circular shape, of a P− type and with a dopinglevel of between 1·10¹⁶ cm⁻³ and 3·10¹⁶ cm⁻³, extends in the secondepitaxial layer 8; in particular, the guard ring 16 gives out onto thetop surface S_(sup) and is arranged on the outside of the anode region12, with which it is in direct contact. Moreover, the guard ring 16 hasa thickness of, for example, between 1 μm and 3 μm.

The guard ring 16 forms a second PN junction with the second epitaxiallayer 8 so as to prevent edge breakdown of the anode region 12.

The detection device 1 further comprises a lateral-insulation region 24,which is arranged on the outside of the guard ring 16 and extends,starting from the top surface S_(sup), within the semiconductor body 3.

The lateral-insulation region 24 has a circular or polygonal shape intop plan view; moreover, the lateral-insulation region 24 extends in thesemiconductor body 3 so as to traverse the first and second epitaxiallayers 6, 8, as well as part of the substrate 2. As mentionedpreviously, the lateral-insulation region 24 surrounds the guard ring 16at a distance.

In turn, the lateral-insulation region 24 comprises a channel-stopperregion 27 arranged further out, formed by dielectric material (forexample, oxide) and arranged in direct contact with the semiconductorbody 3, as well as a barrier region 28, made, for example, of tungsten,which is surrounded by the channel-stopper region 27, with which it isin direct contact.

The detection device 1 further comprises a first dielectric region 30,which extends over the top surface S_(sup), is made, for example, ofthermal oxide and has a thickness of, for example, 0.8 μm. Inparticular, the first dielectric region 30 has a hollow shape so as todefine a cavity that leaves the anode region 12 exposed. In other words,whereas the anode region 12 gives out onto a central portion of the topsurface S_(sup), the first dielectric region 30 extends over aperipheral portion of the top surface S_(sup). Moreover, the firstdielectric region 30 extends partially over the guard ring 16, withwhich it is in direct contact.

The detection device 1 further comprises a region 31, referred tohereinafter as the intermediate region 31.

In detail, the intermediate region 31 is made, for example, ofpolysilicon, is of a P+ type, has a doping level of between 1·10²⁰ cm⁻³and 3·10²⁰ cm⁻³ and has a thickness of, for example, between 50 nm and100 nm. Moreover, the intermediate region 31 extends, in direct contact,on the first dielectric region 30 and on the anode region 12, as well ason the guard-ring portion 16 left exposed by the first dielectric region30.

In greater detail, and without this implying any loss of generality, theintermediate region 31 extends over a central portion of the firstdielectric region 30, which defines the aforementioned cavity, whereasit leaves a peripheral portion of the first dielectric region 30exposed.

The detection device 1 further comprises a second dielectric region 32,which extends, in direct contact, on the intermediate region 31 and onthe peripheral portion of the first dielectric region 30, left exposedby the intermediate region 31. Moreover, the second dielectric region 32has a thickness of, for example, between 50 nm and 500 nm.

In detail, assuming that the detection device 1 is configured to detectthe concentration of a given chemical species (for example, a volatileorganic compound) that comes into contact with the second dielectricregion 32, the second dielectric region 32 is made of any material thatis able to exhibit a variation of its own electrical permittivityfollowing upon interaction with the aforementioned chemical species. Forinstance, the second dielectric region 32 may be made of a material thatexhibits a variation of its own electrical permittivity of at least0.1%, following upon a variation of 50 ppm in the concentration of thechemical species to be detected.

In greater detail, the second dielectric region 32 may be made, forexample, of an oxide of a metal material, such as: TiO₂, V₂O₅, WO₃,SnO₂, ZnO and Fe₂O₃. These materials are characterized by high values ofelectrical permittivity, with consequent increase in the sensitivity ofthe detection device 1; moreover, such materials exhibit lowcoefficients of absorption in the visible and in the ultraviolet, aswell as refractive indices of around 2, i.e., comprised between therefractive index of air and that of silicon, a fact that renders themsuited to forming anti-reflection coatings of the semiconductor body 3.

Alternatively, and once again by way of example, the second dielectricregion 32 may be made, for example, of a non-conductive polymer, or elseof a carbon-based nanomaterial (for example, carbon or graphenenanotubes, possibly functionalized), in which case it may exhibit acertain conductivity. Alternatively, the second dielectric region 32 maybe formed by a polymer/s-metal compound (i.e., a material comprising apolymeric structure with metal inclusions or a metal structureinterspersed by polymer), such as: CFx-Pd, MOF (Metal-OrganicFramework)-5 and Cu₃(btc)₂.

In general, moreover, the second dielectric region 32 can befunctionalized according to the chemical species to be detected.

The detection device 1 further comprises a cathode metallization 42,made of metal material, which extends underneath the bottom surfaceS_(inf) of the substrate 2, with which it is in direct contact. Althoughnot illustrated, the cathode metallization 42 may be formed by acorresponding multilayer structure of metal material.

The detection device 1 further comprises a resistive region 44, whichextends over the second dielectric region 32, as well as, in part,through the second dielectric region 32, so as to contact a portion ofthe intermediate region 31 that extends on the first dielectric region30. The resistive region 44 is delimited at the top by a surface S₄₄,referred to hereinafter as the resistor surface S₄₄.

In particular, the second dielectric region 32 defines a window F, whichoverlies the intermediate region 31; the resistive region 44 extendsthrough the window F so as to contact, in fact, the intermediate region31.

In top plan view, the resistive region 44 has, for example, anelongated, approximately “C” shape, which surrounds, once again in topplan view, the anode region 12, as illustrated, for example in FIG. 3 .For greater clarity, FIG. 3 shows only the anode region 12, the seconddielectric region 32, the resistive region 44, a contact region 46, anda top metallization 48, described hereinafter. Once again without thisimplying any loss of generality, the window F has a quadrangular shapein top plan view.

In greater detail, the resistive region 44 is made, for example, ofpolysilicon of a P type with low doping (for example, of between 1·10¹⁵cm⁻³ and 1·10¹⁶ cm⁻³). Moreover, the portion of resistive region 44 thatextends outside the window F has a thickness of, for example, between300 nm and 700 nm.

The contact region 46 extends in the resistive region 44, starting fromthe resistor surface S₄₄, at a distance from the second dielectricregion 32. The contact region 46 is made, for example, of polysilicon ofa P+ type, has a doping level of between 1·10¹⁹ cm⁻³ and 1·10²⁰ cm⁻³,and has a thickness of, for example, between 0.05 μm and 0.3 μm.

The top metallization 48 is made, for example, of a multilayer structure(not illustrated in detail) of metal material and extends on theresistive region 44, in direct contact with the contact region 46, aswell as with part of the resistive region 44. In addition, without thisimplying any loss of generality, the top metallization 48 has aquadrangular shape in top plan view and overlies entirely the contactregion 46 (detail not shown). Moreover, in top plan view, the topmetallization 48 and the window F are arranged in the proximity of theends of the C shape of the resistive region 44.

For practical purposes, the enriched region 14, the substrate 2, and thefirst and second epitaxial layers 6, 8 form a cathode region. Moreover,the top metallization 48 functions as anode metallization. In addition,in the semiconductor body 3, the avalanche current flows substantiallyin a direction perpendicular to the top surface S_(sup) and to thebottom surface Suf. Moreover, the resistive region 44 is connected inseries to the anode region 12, and hence the avalanche current flowsalso through the resistive region 44.

The second dielectric region 32 functions as sensitive structure, whichinteracts chemically with the chemical species to be detected. Moreover,the second dielectric region 32 is interposed between the intermediateregion 31, which is conductive, and the resistive region 44, whichexhibits in any case a certain capacity of conduction. In particular, asecondary portion of the second dielectric region 32 is covered by theresistive region 44, whereas a main portion of the second dielectricregion 32 is laterally staggered with respect to the resistive region44, and is hence left exposed by the latter so as to be able to interactchemically with the chemical species. This main portion of the seconddielectric region 32 overlies, inter alia, the anode region 12 at adistance.

In other words, the second dielectric region 32, the intermediate region31, and the resistive region 44 form a sort of sensing capacitor, theplates of which, formed respectively by the intermediate region 31 andby the resistive region 44, locally contact one another, in an areacorresponding to the window F. The variations of the electricalpermittivity of the second dielectric region 32, caused by theinteraction with the chemical species, bring about a variation in thecapacitance of the sensing capacitor.

The resistive region 44 moreover acts as quenching resistor, which iselectrically connected to the anode region 12 and is able to quench theavalanche current generated following upon absorption of a photon, asdescribed in greater detail hereinafter.

Operatively, the top metallization 48 is set at a reverse-biasingvoltage V_(A) equal, in modulus, to the sum of the breakdown voltageV_(B) of the junction present between the anode region 12 and thecathode region, plus a voltage V_(OV), of, for example, −3 V. In theabsence of the avalanche current, no current flows in the resistiveregion 44, which is hence all at one and the same voltage, equal to thereverse-biasing voltage V_(A). Following upon triggering of theavalanche current, within the resistive region 44 a potential dropoccurs on account of the flow of the avalanche current within theresistive region 44. In particular, whereas the portion of resistiveregion 44 that contacts the top metallization 48 remains at thereverse-biasing voltage V_(A), the portion of resistive region 44 thatcontacts the intermediate region 31 is at a voltage approximately equalto the breakdown voltage V_(B). Following upon quenching of theavalanche current, the resistive region 44 returns to having all one andthe same voltage, equal to the reverse-biasing voltage V_(A). In otherwords, the anode region 12 recharges to the reverse-biasing voltageV_(A), with a timing that depends, not only upon the value of resistanceof the resistive region 44, but also upon the capacitance of the sensingcapacitor.

As regards, instead, the lateral-insulation region 24, it enables, bymeans of the barrier region 28, optical insulation of the detectiondevice 1 from the other detection devices of the array 220. Inparticular, the barrier region 28 of the lateral-insulation region 24enables reduction of instantaneous crosstalk. Moreover, the oxidepresent in the channel stopper 27 guarantees electrical insulation.

In use, turning-on of a detection device 1 does not alter, to a firstapproximation, biasing of the adjacent detection devices 1. In addition,within the substrate 2, the voltage drop due to the passage of theavalanche current is negligible, on account of the low resistivity ofthe substrate 2. Consequently, the array 220 forms a so-called siliconphotomultiplier (SiPM), i.e., an array of SPADs (in the case in point,the detection devices 1), grown on one and the same substrate andprovided with respective quenching resistors decoupled from andindependent of one another. Moreover, the detection devices 1 areconnected to one and the same voltage generator (not illustrated) so asto be biased at the aforementioned reverse-biasing voltage V_(A). Theavalanche currents generated within the detection devices 1 aremultiplexed together so as to generate a signal at output from the SiPM,referred to hereinafter as “array signal”. The array signal is equal tothe summation of the output signals of the SPADs, which are formed bythe avalanche currents. The array signal is hence proportional, to afirst approximation, to the number of photons that impinge upon thearray 220.

This having been said, FIG. 4A shows possible time plots of the arraysignal corresponding to different values of the capacitance of theaforementioned sensing capacitor.

In particular, it may be noted how, as the value of capacitance of thesensing capacitor increases, and other conditions (for example, biasing)being equal, there is an increase in the peak value of the current pulseof the array signal, as well as an increase in the slope of theso-called rising portion of the pulse, which precedes occurrence of thepeak. In addition, as is more clearly visible in FIG. 4B, as the valueof capacitance of the sensing capacitor increases, there is an increasein the duration of the so-called quenching portion of the pulse, i.e.,of the portion of the pulse immediately subsequent to the peak andhaving a decreasing exponential trend, that precedes the so-calledrecharging portion, which follows an approximately rectilinear pattern.The dependence of the duration of the quenching portion of the pulseupon the value of capacitance of the sensing capacitor is greater thanthe dependence of the slope of the rising portion of the pulse upon thesame quantity.

In other words, modulation of the capacitance of the sensing capacitorenables modulation of the pattern of the array signal. In turn, asexplained previously, the capacitance of the sensing capacitor dependsupon the concentration of at least one chemical species (for example, inthe gaseous state), which interacts with the detection device 1, and inparticular with the second dielectric region 32. For this reason, thedetection device 1 functions as electrical transducer of theconcentration of the chemical species.

In greater detail, it is possible to make use of the detection system110 illustrated in FIG. 5 , which comprises, in addition to the array220, appropriately supplied by a corresponding power-supply stage (notillustrated), also a pre-amplifier 106 (optional), a fixed-thresholddiscriminator (FTD) 108, a time-to-amplitude converter (TAC) 120, acomputer 122, and a screen 124.

The array 220 is electrically connected to the input of thepre-amplifier 106, the output of which is connected to the input of thefixed-threshold discriminator 108; a first output of the fixed-thresholddiscriminator 108 is connected to a first input terminal START of thetime-to-amplitude converter 120, whereas a second output of thefixed-threshold discriminator 108 is connected to a second inputterminal STOP of the time-to-amplitude converter 120, the output ofwhich is connected to the computer 122, which in turn is connected tothe screen 124.

In use, the pre-amplifier 106 amplifies the array signal, generating apre-amplified signal. The fixed-threshold discriminator 108 generates,on its own first output, a first timing signal, indicating the instantwhen the current value of each pulse (in particular, the rising portion)of the pre-amplified signal exceeds a threshold value. Moreover, thefixed-threshold discriminator 108 generates, on its own second output, asecond timing signal, indicating the instant when the current value ofeach pulse (in particular, of the quenching portion) of thepre-amplified signal drops below the threshold value.

As mentioned previously, the instant when the current value of eachpulse of the pre-amplified signal exceeds the threshold value mayindicate detection of a photon by the detection device 1. However, thisaspect is irrelevant for the purposes of determination of theconcentration of the chemical species under examination, as explained indetail hereinafter. In this connection, here it is anticipated thattriggering of a current pulse can occur also independently of thepresence of radiation. In other words, for the purposes of determinationof the concentration it is irrelevant what type of event leads totriggering of the current pulses, which can hence be formed by so-calleddark pulses. In what follows, for a generic current pulse of thepre-amplified signal reference is made to the first and second instantst₁, t₂ to indicate, respectively, the instant when the current exceedsthe threshold value and the subsequent instant when the current dropsbelow the threshold value.

Irrespective of the cause that has led to generation of a pulse of thearray signal, it may be demonstrated that, given a current pulse of thearray signal, dependence of the corresponding first instant t₁ upon thevalue of capacitance of the sensing capacitors is substantiallynegligible, given that it is in the region of 0.2 ps for a variation ofcapacitance of 1%; instead, dependence of the corresponding secondinstant t₂ upon the value of capacitance of the sensing capacitors issignificant, given that it is approximately 10 ps for a variation ofcapacitance of 1%.

This having been said, the time-to-amplitude converter 120 generates, asa function of the first and second timing signals, a respective outputsignal, which represents, for each pulse of the array signal, theduration of the time interval that elapses between the correspondingfirst and second instants t₁, t₂, this duration being referred tohereinafter as the duration of the over-threshold interval. The computer122 can thus calculate an estimate of the concentration of the chemicalspecies that interacts with the second dielectric region 32 on the basisof the output signal.

In detail, the computer 122 can initially calculate a value ofcapacitance of the sensing capacitor, for example on the basis of afirst calibration curve, an example of which is illustrated in FIG. 6 .In detail, the first calibration curve is determined experimentally andis stored by the computer 122. Moreover, the first calibration curvecorrelates the variation of the duration of the over-threshold interval(measured with respect to a reference duration) with the variation ofthe capacitance of the sensing capacitor (measured with respect to areference capacitance).

Next, the computer 122 can determine the concentration of the chemicalspecies under examination, on the basis of the aforementioned variationof the capacitance and, for example, on the basis of a secondcalibration curve, which correlates the variation of concentration ofthe chemical species (measured with respect to a referenceconcentration) with the variation of the capacitance of the sensingcapacitor. Also the second calibration curve can be determinedexperimentally. Alternatively, the computer 122 can determine theconcentration of the chemical species under examination as a function ofthe duration of the over-threshold interval and of a third calibrationcurve determined experimentally, which correlates the concentration ofthe chemical species under examination and the duration of theover-threshold interval.

Finally, the computer 122 displays the value of concentration determinedon the screen 124.

Various embodiments are moreover possible, as illustrated, for examplein FIG. 7 . In this case, extending over the second dielectric region32, and in particular over the portion of the second dielectric region32 that overlies, at a distance, the anode region 12, is an additionalregion 51, made of metal material (for example, palladium, tungsten, oriridium).

The additional region 51 has a thickness of, for example, between 50 nmand 500 nm and forms a sensitive structure with the second dielectricregion 32.

Operatively, the additional region 51 functions as precursor, in orderto increase the chemical interaction between the underlying seconddielectric region 32 and the chemical species under examination, whichcan be represented, for example, by molecular hydrogen. Moreover, asexplained previously, the fact that the additional region 51 can shieldthe radiation does not affect the behavior of the detection device 1.

Albeit not illustrated, embodiments are moreover possible, which are thesame as the embodiments illustrated in FIGS. 1 and 7 , respectively, butin which the intermediate region 31 is absent, as illustrated, forexample in FIG. 8 . However, the presence of the intermediate region 31enables reduction of the defectiveness of the anode region 12 since itavoids having to resort, during manufacture of the anode region 12, toprocesses of implantation.

Embodiments are moreover possible, in which, between the seconddielectric region 32 and, if present, the intermediate region 31, orelse the anode region 12, if the intermediate region 31 is absent, alayer 53 is present, referred to in what follows as the supporting layer53. An example of such embodiments, referred to the case where theintermediate region 31 is present, is illustrated in FIG. 9 . The windowF also extends through the supporting layer 53.

In detail, the supporting layer 53 is made, for example, of siliconoxide (SiO₂), or else of silicon nitride (Si₃N₄) and performs thefunction of reducing the surface defectiveness.

Albeit not illustrated, embodiments are moreover possible, which includeboth the additional region 51 and the supporting layer 53.

Embodiments are moreover possible present in which are one or moreadditional sensitive regions, as illustrated, for example, in FIG. 10 .In particular, FIG. 10 shows a third dielectric region 57, whichoverlies, in direct contact, the second dielectric region 32. The windowF also extends through the third dielectric region 57, which in top planview can have the same shape as the underlying second dielectric region32. Moreover, the resistive region 44 extends over the third dielectricregion 57.

In detail, the third dielectric region 57 may be made of any one of thematerials mentioned previously with reference to the second dielectricregion 32, provided that it is different from the material that formsthe second dielectric region 32. In this way, whereas the seconddielectric region 32 exhibits a variation of the electrical permittivityas a function of the concentration of a first chemical species, thethird dielectric region 57 exhibits a variation of the electricalpermittivity as a function of the concentration of a second chemicalspecies.

Albeit not illustrated, further embodiments are moreover possible,present in which more than two sensitive regions are present, stacked ontop of one another, within a multilayer structure.

The present detection device 1 may be manufactured following themanufacturing method that is described hereinafter, with particularreference, purely by way of example, to an embodiment of the typeillustrated in FIG. 1 , but in which the lateral-insulation region 24 isabsent.

As illustrated in FIG. 11 , formed in a way in itself known are thesubstrate 2, the first and second epitaxial layers 6, 8, the enrichedregion 14, the guard ring 16, and the first dielectric region 30.

Next, as illustrated in FIG. 12 , the intermediate region 31 is formed,for example by means of a process of deposition of a polysilicon layerdoped in situ and a subsequent photolithographic process.

Then, as illustrated in FIG. 13 , formed by deposition is a layer 32′,referred to hereinafter as the first process layer 32′. The firstprocess layer 32′ is to form the second dielectric region 32. Purely byway of example, the first process layer 32′ may be made of TiO₂ and havea thickness of 200 nm.

Next, as illustrated in FIG. 14 , a thermal annealing is carried out ata temperature of, for example, 1000° C., and with a duration of, forexample, 90 s. The aforesaid annealing causes formation of the anoderegion 12.

Then, as illustrated in FIG. 15 , a further photolithographic process iscarried out, using a corresponding mask (not illustrated), so as toremove selectively a portion of the first process layer 32′ and form thewindow F. The remaining portion of the first process layer 32′ forms thesecond dielectric region 32.

Next, as illustrated in FIG. 16 , a layer 44′, referred to hereinafteras the second process layer 44′, is formed by deposition. The secondprocess layer 44′ is made of non-doped polysilicon and is to form theresistive region 44. Purely by way of example, the second process layer44′ may have a thickness of 500 nm. Moreover, deposition of thepolysilicon may be carried out at a temperature of approximately 600° C.

Then, as illustrated in FIG. 17 , a further thermal annealing is carriedout at a temperature of, for example, 950° C., and with a duration of,for example, 10 min. This annealing causes formation of an oxide layer59 on the second process layer 44′. The oxide layer 59 has a thicknessof, for example, 50 nm.

Next, as illustrated once again in FIG. 17 , an ion implantation(indicated by the arrows 61) of dopant species of a P type (for example,boron) is carried out, with a doping of, for example, 1.4·10¹⁴ cm⁻² andan energy of, for example, 50 keV. This implantation causes the secondprocess layer 44′ to acquire the doping level of the resistive region44.

Then, as illustrated in FIG. 18 , a process of selective ionimplantation (indicated by the arrows 63) of dopant species of a P type(for example, boron) is carried out, with the aid of a correspondingmask (not illustrated), with a doping of, for example, 5·10¹⁴ cm⁻² andan energy of, for example, 50 keV, so as to form the contact region 46.The mask is subsequently removed, and then a further thermal annealingis carried out in a nitrogen environment, at a temperature of, forexample, 1000° C. and with a duration of, for example, half an hour.

Next, as illustrated in FIG. 19 , the oxide layer 59 is removed, forexample by means of a wet etch.

Then, as illustrated in FIG. 20 , a further photolithographic process iscarried out, using a corresponding mask (not illustrated), which enablesselective removal of portions of the second process layer 44′. Theremaining portion of the second process layer 44′ forms the resistiveregion 44.

The detection device 1 is then completed in a way in itself known.

From what has been described and illustrated previously, the advantagesthat the present solution affords are evident.

In particular, the present device enables detection of theconcentrations of one or more chemical species, with a high sensitivity,without having to resort to the use of a heater. In this connection, ithas been found that the present detection device has a sensitivity inthe region of 0.1%; it hence enables, for example, detection of aconcentration of ammonia in the region of 5 ppm, in the case where thesensitive structure includes at least one nafion region.

In addition, the presence of a Geiger-mode diode enables amplificationof the detection signal, without any need to resort to furtherintegrated devices. Moreover, since the sensitive region is nottraversed by current, effects of hysteresis are prevented, as well asdeterioration of the performance of the detection device.

Finally, it is clear that modifications and variations may be made towhat has been described and illustrated herein, without therebydeparting from the sphere of protection of the present disclosure, asdefined in the annexed claims.

As mentioned previously, the intermediate region 31 may be absent, aslikewise the lateral-insulation region 24. Moreover, in the limit, it ispossible for the die 100 to comprise just one detection device 1.

As regards the second dielectric region 32, it may be made of the samematerials described previously, but of a porous or nanostructured typein order to increase sensitivity.

Also the manufacturing method may differ from what has been described.Purely by way of example, the anode region 12 may be formed byimplantation instead of by diffusion.

Finally, all the types of doping may be reversed with respect to whathas been described.

The various embodiments described above can be combined to providefurther embodiments. These and other changes can be made to theembodiments in light of the above-detailed description. In general, inthe following claims, the terms used should not be construed to limitthe claims to the specific embodiments disclosed in the specificationand the claims, but should be construed to include all possibleembodiments along with the full scope of equivalents to which suchclaims are entitled. Accordingly, the claims are not limited by thedisclosure.

The invention claimed is:
 1. A method for manufacturing a device fordetecting a chemical species, comprising: forming a Geiger-modeavalanche diode in a body of semiconductor material delimited by a frontsurface, wherein forming the Geiger-mode avalanche diode includes:forming a cathode region having a first type of conductivity in the bodyand extending from the front surface; and forming an anode region havinga second type of conductivity, which extends in the cathode regionstarting from the front surface; forming, on the anode region, asensitive structure that includes a sensitive region, said sensitiveregion having an electrical permittivity that depends upon aconcentration of said chemical species, a portion of the sensitiveregion directly overlying the anode region; and forming, on thesensitive structure, a resistive region electrically coupled to theanode region.
 2. The method of claim 1, further comprising: forming, onthe resistive region, a contact region electrically coupled to theresistive region.
 3. The method of claim 2 wherein forming the resistiveregion includes forming the resistive region with an elongated shapewith a first end and a second end, the first end being electricallycoupled to the anode region, the second end being electrically coupledto the contact region.
 4. The method of claim 1, further comprising:forming, between the anode region and the sensitive structure, anintermediate semiconductor region having the second type ofconductivity, the intermediate semiconductor region being electricallyinterposed between the resistive region and the anode region.
 5. Themethod of claim 4 wherein forming the anode region includes, afterforming the cathode region, forming the intermediate semiconductorregion.
 6. The method of claim 1 wherein the sensitive region is made ofa material chosen from a group consisting of: an oxide of a metalmaterial, a non-conductive polymer, a carbon-based nanomaterial, and apolymer-metal compound.
 7. The method of claim 1, further comprising:forming a precursor layer of metal material on the sensitive region, theprecursor layer being configured to increase a chemical interactionbetween the sensitive region and the chemical species.
 8. The method ofclaim 1, further comprising: forming a bottom metallization arrangedunderneath the body.
 9. The method of claim 1 wherein the first type ofconductivity is a conductivity of an N type, and the second type ofconductivity is a conductivity of a P type.
 10. A method, comprising:forming a cathode region of a first type of conductivity in a substrate,the cathode region extending from a surface of the substrate; forming ananode region of a second type of conductivity, the anode regionextending in the cathode region from the surface of the substrate;forming a sensitive structure on the anode region, the sensitivestructure including a sensitive region having an electrical permittivitythat depends upon a concentration of a chemical species, a portion ofthe sensitive region directly overlying the anode region; and forming aresistive region on the sensitive structure, the resistive region beingelectrically coupled to the anode region.
 11. The method of claim 10,further comprising: forming a contact region that extends over and iselectrically coupled to the resistive region, the resistive regionhaving an elongated shape with a first end and a second end, the firstend being electrically coupled to the anode region, the second end beingelectrically coupled to the contact region.
 12. The method of claim 10,further comprising: forming an intermediate semiconductor region havingthe second type of conductivity, the intermediate semiconductor regionbeing interposed between the anode region and the sensitive structure,the resistive region being electrically coupled to the anode regionthrough the intermediate semiconductor region.
 13. The method of claim10, further comprising: forming a precursor layer of metal material onthe sensitive region, the precursor layer being configured to increase achemical interaction between the sensitive region and the chemicalspecies.
 14. The method of claim 10 wherein the sensitive region is madeof a material chosen from a group consisting of: an oxide of a metalmaterial, a non-conductive polymer, a carbon-based nanomaterial, and apolymer-metal compound.
 15. The method of claim 10 wherein the firsttype of conductivity is a conductivity of an N type, and the second typeof conductivity is a conductivity of a P type.
 16. A method, comprising:forming a cathode region in a substrate, the cathode region having afirst type of conductivity; forming an anode region that extends in tothe cathode region, the anode region having a second type ofconductivity; forming a sensitive structure on the anode region, thesensitive structure including a sensitive region that is sensitive to achemical species, a portion of the sensitive region directly overlyingthe anode region; and forming a resistive region on the sensitivestructure, the resistive region being electrically coupled to the anoderegion, the anode region being positioned between first and secondportions of the resistive region.
 17. The method of claim 16 wherein theportion of the sensitive region is between the first and second portionsof the resistive region.
 18. The method of claim 16 wherein forming theresistive region includes forming the resistive region along threedifferent sides of the anode region.
 19. The method of claim 16, furthercomprising: forming a precursor layer on the sensitive region, theprecursor layer being configured to increase a chemical interactionbetween the sensitive region and the chemical species.